Method for calculating thickness of doped semiconductor layer by utilizing reflection spectrum fitting

Abstract

The invention relates to a method for calculating the thickness of a doped semiconductor layer by utilizing reflection spectrum fitting, which comprises the following steps of: inputting the reflection spectrum of one or more doped semiconductor layers on a wafer into a mathematical relationship model of reflectivity and thickness, and setting the number of the doped semiconductor layers, the parameters comprise the number of doped semiconductor layers, and the carrier concentration, carrier mobility and thickness of each doped semiconductor layer, and the target value is the reflectivity; and fitting the theoretical spectrum calculated by the mathematical relationship model of the reflectivity and the thickness with the reflection spectrum by adjusting the carrier concentration, the carrier mobility and the thickness of each doped semiconductor layer, and outputting the carrier concentration, the carrier mobility and the thickness. According to the method, the thickness of each doped semiconductor layer can be obtained without damaging the sample.

Description

Technical Field

[0001] The invention relates to the technical field of epitaxial layer detection, and in particular to a method for calculating the thickness of a doped semiconductor layer by using reflection spectrum fitting. Background Art

[0002] Inspection of epitaxial layer and buffer layer thickness is an important step in the semiconductor manufacturing process and is critical to ensuring product quality and performance.

[0003] Currently, for the wafer structure of substrate + buffer layer + one or more epitaxial layers, the methods for detecting the thickness of the buffer layer and the epitaxial layer include secondary ion mass spectrometer SIMS detection, scanning electron microscope (SEM) detection and spread resistance test (SRP) technology detection, but these methods are destructive to the samples.

[0004] Although infrared reflectometry (FTIR) can detect epitaxial thickness non-destructively, it is difficult to distinguish multilayer structures and cannot accurately measure the single-layer thickness of the buffer layer and epitaxial layer. Summary of the invention

[0005] In order to solve at least part of the above problems in the prior art, the present invention provides a method for calculating the thickness of a doped semiconductor layer by using reflection spectrum fitting, comprising:

[0006] Inputting the reflection spectrum of one or more doped semiconductor layers on the wafer into a mathematical relationship model between reflectivity and thickness, and setting the number of doped semiconductor layers, wherein: in the mathematical relationship model between reflectivity and thickness, the parameters include the number of doped semiconductor layers, the carrier concentration, the carrier mobility and the thickness of each doped semiconductor layer, and the target value is the reflectivity; and

[0007] By adjusting the carrier concentration, carrier mobility and thickness of each doped semiconductor layer, the theoretical spectrum calculated by the mathematical relationship model of reflectivity and thickness is fitted with the reflectance spectrum, and the carrier concentration, carrier mobility and thickness are output.

[0008] Furthermore, in the mathematical relationship model between reflectivity and thickness, the complex dielectric function is calculated from the carrier concentration and the carrier mobility, the complex refractive index is calculated from the complex dielectric function, and the reflectivity is calculated from the complex refractive index and the thickness of the doped semiconductor layer.

[0009] Further, the complex refractive index of each doped semiconductor layer is calculated using the complex dielectric function of each doped semiconductor layer, and the characteristic matrix of each doped semiconductor layer is calculated from the complex refractive index and thickness of each doped semiconductor layer;

[0010] The overall characteristic matrix is ​​obtained by multiplying the characteristic matrices of each doped semiconductor layer;

[0011] The overall characteristic matrix is ​​multiplied by the incident light to obtain the outgoing light, and the outgoing light is used to calculate the total reflection coefficient, and then the total reflectivity is calculated from the reflection coefficient.

[0012] Further, calculating the complex refractive index of each doped semiconductor layer using the complex dielectric function of each doped semiconductor layer comprises:

[0013] where ∈(ω) is the complex dielectric function, ∈ ∞ is the high frequency dielectric constant, ω p is the plasma frequency, γ is the plasma damping coefficient, ω is the angular frequency of the light wave (ω=2πf), ω is known;

[0014] Where N is the carrier concentration, e is the electron charge, m* is the effective mass, ε ∞ is the high frequency dielectric constant, ε0 is the vacuum dielectric constant; and

[0015] where μ is the carrier mobility.

[0016] Furthermore, for a single doped semiconductor layer, the optical path δ j With wavelength λ, material thickness d j , angle of incidence α j The relationship is When the light wave passes through a single-layer doped semiconductor layer, the light wave With the emitted light wave The relationship is is defined as the characteristic matrix of a doped semiconductor, where:

[0017] For TE mode, γ j =n j cosα j , δ j =ωn j d j cosα j / c

[0018] For TM modules: γ j =n j cosα j , δ j =ωn j d j cosα j / c

[0019] in,

[0020] α0 is the incident angle, ω is the angular frequency of light, c is the speed of light, d jis the thickness of the corresponding doped semiconductor layer, n j is the refractive index of the corresponding doped semiconductor layer, n0 is the refractive index of air, j is the number of layers corresponding to the multilayer doped semiconductor layer, δ j It is the optical path length of each layer corresponding to the multilayer film.

[0021] Furthermore, for multiple doped semiconductor layers, the characteristic matrix of each layer is calculated first, and then the overall characteristic matrix M is obtained by multiplying them. tot , the feature matrix M tot Multiplying the incident light by the outgoing light Where N is a positive integer;

[0022] The total reflection coefficient is given by the following relationship:

[0023]

[0024] The total reflectivity is calculated from the total reflection coefficient: R = |r| 2 .

[0025] Furthermore, the carrier concentration, carrier mobility and thickness of each doped semiconductor layer are automatically adjusted using a least square method or a genetic algorithm.

[0026] Furthermore, before the step of inputting the reflection spectrum into the mathematical relationship model of reflectivity and thickness, the step also includes: obtaining the reflection spectrum of one or more doped semiconductor layers on the wafer.

[0027] Further, obtaining a reflectance spectrum of one or more doped semiconductor layers on a wafer includes:

[0028] Using a Fourier transform infrared spectrometer to measure the interference spectrum of the wafer and the interference spectrum of the reference piece;

[0029] Converting the interference spectrum of the wafer and the interference spectrum of the reference piece into corresponding single-beam spectrum of the wafer and single-beam spectrum of the reference piece by Fourier transform; and

[0030] The reflection spectrum of one or more doped semiconductor layers is obtained by subtracting the ordinate of the single beam spectrum of the reference wafer from the ordinate of the single beam spectrum of the wafer.

[0031] Furthermore, the one doped semiconductor layer is a buffer layer, and the multiple doped semiconductor layers are a buffer layer and a single epitaxial layer or a buffer layer and a double epitaxial layer.

[0032] The present invention has at least the following beneficial effects: the method for calculating the thickness of a doped semiconductor layer by using a reflection spectrum fitting provided by the present invention inputs the measured reflection spectrum into a mathematical relationship model between reflectivity and thickness, and by adjusting the three parameters of the carrier concentration, carrier mobility and thickness of each doped semiconductor layer, the theoretical spectrum calculated by the mathematical relationship model between reflectivity and thickness is fitted with the reflection spectrum, so that the reflectivity of the theoretical spectrum and the reflectivity of the reflection spectrum are as equal as possible, and the thickness of each doped semiconductor layer can be obtained. This method can obtain the thickness of each doped semiconductor layer without damaging the sample. Moreover, the carrier concentration and the carrier mobility can be obtained at the same time by this method. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to further illustrate the above and other advantages and features of various embodiments of the present invention, a more specific description of various embodiments of the present invention will be presented with reference to the accompanying drawings. It will be understood that these drawings only depict typical embodiments of the present invention and are therefore not to be considered as limiting the scope thereof. In the accompanying drawings, for clarity, identical or corresponding parts will be represented by identical or similar reference numerals.

[0034] Figure 1 The flowchart of a method for calculating the thickness of a doped semiconductor layer by using reflection spectrum fitting according to an embodiment of the present invention is shown.

[0035] Figure 2 A comparison between the fitted thickness of a double-layer structure according to an embodiment of the present invention and a reference thickness value is shown.

[0036] Figure 3 A comparison diagram of the fitted thickness and the reference thickness value of a three-layer structure sampled at a single point according to an embodiment of the present invention is shown.

[0037] Figure 4 A comparison diagram of the fitted thickness and reference thickness values ​​of a three-layer structure sampled at multiple points according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0038] It should be noted that various components in the various drawings may be shown exaggeratedly for illustrative purposes and are not necessarily correct to scale.

[0039] In the present invention, each embodiment is only intended to illustrate the aspects of the present invention and should not be construed as limiting.

[0040] In the present invention, unless otherwise specified, the quantifiers "a", "an" and "an" do not exclude the presence of a plurality of elements.

[0041] It should also be pointed out that in the embodiments of the present invention, for the sake of clarity and simplicity, only a portion of the parts or components may be shown, but a person of ordinary skill in the art will understand that under the teachings of the present invention, required parts or components may be added as needed in specific scenarios.

[0042] It should also be pointed out that within the scope of the present invention, the terms "same", "equal", "equal to" and the like do not mean that the two values ​​are absolutely equal, but allow a certain reasonable error, that is, the terms also cover "substantially the same", "substantially equal", and "substantially equal to".

[0043] It should also be pointed out that in the description of the present invention, the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than explicitly or implicitly indicating that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as explicitly or implicitly indicating relative importance.

[0044] In addition, the embodiments of the present invention describe the process steps in a specific order, but this is only for the convenience of distinguishing the steps, and does not limit the sequence of the steps. In different embodiments of the present invention, the sequence of the steps can be adjusted according to the adjustment of the process.

[0045] Figure 1 The flowchart of a method for calculating the thickness of a doped semiconductor layer by using reflection spectrum fitting according to an embodiment of the present invention is shown.

[0046] Step 1, obtaining the reflection spectrum of one or more doped semiconductor layers on the wafer. The doped semiconductor layer may be a buffer layer or an epitaxial layer. The multi-layer doped semiconductor layer may be a buffer layer + an epitaxial layer or a buffer layer + a double epitaxial layer. Here, for the multi-layer doped semiconductor layer, the reflection spectrum here is the total reflection spectrum of the multi-layer doped semiconductor layer, rather than the reflection spectrum of a single-layer structure.

[0047] First, the interference spectrum of the sample and the reference piece are measured using a Fourier transform infrared spectrometer (FTIR), and then converted into the corresponding single-beam spectrum of the sample and the single-beam spectrum of the reference piece by Fourier transform. The ordinate of the interference spectrum is the light signal intensity Voltage, and the abscissa is the optical path difference. The ordinate of the single-beam spectrum is the absorbance, and the abscissa is the wave number.

[0048] The single-beam spectrum of the sample is subtracted from the single-beam spectrum of the reference film, that is, the vertical coordinates of the two are subtracted to obtain the reflectance spectrum of the sample.

[0049] Since the sample is a wafer and the structure is substrate + doped semiconductor layer, the single-beam spectrum of the sample is subtracted from the single-beam spectrum of the reference wafer in order to remove the spectrum of the substrate and retain the spectrum of the doped semiconductor layer.

[0050] Step 2, input the reflection spectrum into the mathematical relationship model of reflectivity and thickness, and set the number of doped semiconductor layers. The parameters include the number of doped semiconductor layers, the carrier concentration, carrier mobility and thickness of each doped semiconductor layer. The target value is the reflectivity. The number of doped semiconductor layers can be set.

[0051] Step 3, by adjusting the carrier concentration, carrier mobility and thickness of each doped semiconductor layer in the model to fit the theoretical spectrum calculated by the model with the reflection spectrum, and outputting the carrier concentration, carrier mobility and thickness at this time.

[0052] The number of doped semiconductor layers has been set. By adjusting the carrier concentration, carrier mobility and thickness of each doped semiconductor layer in the model, the reflectivity of the theoretical spectrum calculated by the model is made as equal as possible to the reflectivity of the reflection spectrum, with the smallest difference, so that the theoretical spectrum and the reflection spectrum are optimally fitted, and the carrier concentration, carrier mobility and thickness at this time are output. During the fitting process, the reflectivity of the reflection spectrum is used as the standard value, and the parameters are continuously adjusted to make the reflectivity of the theoretical spectrum close to the reflectivity of the reflection spectrum.

[0053] Optimization algorithms such as the least squares method and genetic algorithm can be used to automatically adjust parameters and improve fitting accuracy.

[0054] In order to verify the accuracy of the results, the actual thickness value measured by the SIMS method can also be compared with the thickness value calculated by fitting.

[0055] The theoretical basis of the mathematical relationship model between reflectivity and thickness is introduced in detail below.

[0056] 1. Effect of doping on band structure

[0057] Doping Type: Doping can be either n-type (donating extra electrons) or p-type (donating holes).

[0058] Band changes: Doping introduces impurity energy levels into the band gap or changes the filling of the conduction band and valence band.

[0059] Carrier concentration: Doping increases the concentration of free charge carriers, which can participate in conductive and optical transitions.

[0060] 2. Dielectric function and optical properties

[0061] The complex dielectric function ∈(ω)=∈1(ω)+i∈2(ω) is the key parameter to describe the optical response of the material, where: ∈1(ω) is the real part, which is related to the refractive index n and extinction coefficient k of the material: ∈1=n 2 -k 2 ;

[0062] ∈2(ω) is the imaginary part, which is directly related to the absorption characteristics of the material: ∈2=2nk.

[0063] The complex refractive index n(ω) consists of the refractive index n and the extinction coefficient k: n(ω)=n+ik

[0064] The relationship between the complex dielectric function and the complex refractive index is: (n+ik) 2 =∈(ω).

[0065] The complex refractive index n(ω) can be calculated from the complex dielectric function ∈(ω).

[0066] 3. Calculation of complex dielectric function

[0067] For doped semiconductors, the complex dielectric function ∈(ω) can be calculated using a theoretical model:

[0068]

[0069] Among them, ∈∞ is the high frequency dielectric constant, ω p is the plasma frequency (related to the carrier concentration), γ is the plasma damping coefficient (related to the carrier mobility), ω is the angular frequency of the light wave, and ω is known.

[0070] Where N is the carrier concentration, e is the electron charge, m* is the electron effective mass, ε ∞ is the high frequency dielectric constant, ε0 is the vacuum dielectric constant, e, m*, ε ∞ , ε0 are known parameters. The plasma frequency is determined by the carrier concentration and the effective mass of electrons. In semiconductor materials, changes in carrier concentration will cause changes in the dielectric constant, which in turn affects the plasma frequency.

[0071] Where μ is the carrier mobility. The plasma damping coefficient γ is determined by the carrier mobility and the electron effective mass m*. The change of carrier mobility will affect the plasma damping coefficient.

[0072] The complex dielectric function can be calculated from the carrier concentration and mobility.

[0073] 4. Calculate the reflectance of the theoretical spectrum

[0074] The complex dielectric function can be calculated from the carrier concentration and carrier mobility, the complex refractive index n(ω) can be calculated from the complex dielectric function, and the reflectivity can be calculated from the complex refractive index and material thickness. Therefore, changing the carrier concentration, carrier mobility and thickness will change the reflectivity.

[0075] The complex refractive index of each doped semiconductor layer is calculated using the complex dielectric function of each doped semiconductor layer, and the characteristic matrix of each doped semiconductor layer is calculated by the complex refractive index and thickness of each doped semiconductor layer. The overall characteristic matrix M of the multilayer structure is obtained by multiplying multiple characteristic matrices. tot , the overall characteristic matrix is ​​multiplied by the incident light to obtain the outgoing light, and the total reflection coefficient is calculated using the outgoing light, and finally the total reflectivity is obtained.

[0076] In a single-layer medium, the optical path length δ j With wavelength λ, material thickness d j , angle of incidence α j The relationship is When light waves pass through a single layer of medium, With the emitted light wave The relationship is is defined as the characteristic matrix of the dielectric layer, where i is an imaginary number, γ j Related to the refractive index and incident angle of the medium layer, for the TE mode (transverse mode, corresponding to s-wave):

[0077] γ j =n j cosα j , δ j =ωn j d j cosα j / c

[0078] For TM mode (longitudinal mode, corresponding to p wave):

[0079] For TM modules: γ j =n j cosα j , δ j =ωn j d j cosα j / c

[0080] in,

[0081] α0 is the angle of incidence, c is the speed of light, d j is the corresponding dielectric layer thickness, n j is the refractive index of the corresponding dielectric layer, n0 is the refractive index of air (the reference value is 1), j is the number of layers corresponding to the multi-layer dielectric layer, for a single dielectric layer, j = 1, δ jis the optical path length of each layer corresponding to the multi-layer dielectric layer, γ j It is a reference value and has no practical significance. In the present invention, the dielectric layer refers to a doped semiconductor layer, such as a buffer layer or an epitaxial layer.

[0082] For a multilayer dielectric structure, the characteristic matrix M of each layer can be calculated first j , after multiplication, we get the overall characteristic matrix M of the multilayer medium tot , M tot Multiplying the incident light by the outgoing light Where N is a positive integer;

[0083] The reflection coefficient of the multilayer film structure can be obtained from the following relationship.

[0084]

[0085] Finally, the reflectivity of the multilayer film structure is R = |r| 2 .

[0086] Except for the carrier concentration, carrier mobility and thickness, the other parameters involved in the model are known, because changing the carrier concentration, carrier mobility and thickness will change the reflectivity.

[0087] The present invention also provides a computer system, comprising: a processor configured to execute machine executable instructions; a memory storing machine executable instructions, which, when executed by the processor, executes the steps of a method for calculating the thickness of a doped semiconductor layer using reflectance spectrum fitting.

[0088] In actual operation, before fitting the reflectance spectrum with the theoretical spectrum calculated by the model, select the band range to be fitted, usually 1200-3000cm -1 , set the number of layers of the doped semiconductor structure and set the incident angle.

[0089] Furthermore, a corresponding structure, such as substrate+buffer layer+epitaxial layer, may be constructed according to the design structure of the doped semiconductor structure.

[0090] Furthermore, the maximum / minimum value and the baseline value of the thickness of the corresponding doped semiconductor structure may be set according to the design of the SiC wafer.

[0091] Then, the algorithm automatically adjusts the carrier concentration, carrier mobility and thickness of each doped semiconductor layer in the model to fit the theoretical spectrum calculated by the model with the reflection spectrum, and outputs the carrier concentration, carrier mobility and thickness at this time.

[0092] For products produced in the same batch, their structural designs are the same, and the carrier concentration and carrier mobility remain basically unchanged, which can be set as constant values. Only the thickness value needs to be adjusted for fitting. In this way, the measured thickness of each corresponding layer is more stable and reliable.

[0093] Figure 2 A comparison between the fitted thickness of a double-layer structure according to an embodiment of the present invention and a reference thickness value is shown.

[0094] For a buffer layer + single epitaxial layer structure, Figure 2 The thickness values ​​obtained from 10 fits are shown, and the average values ​​of the buffer layer thickness and the total thickness of the double-layer structure obtained from the 10 fits are compared with the reference thickness measured by the SIMS method.

[0095] The average total thickness of the double-layer structure is 13.126um, the reference thickness is 13.176um, the difference is 0.05um, the average buffer layer thickness is 3.26um, the reference thickness is 3.292um, the difference is 0.03um, and the difference between the fitted thickness and the reference thickness is less than 0.1um.

[0096] It can be seen from the above verification results that the method of the present invention can accurately obtain the thickness of the multi-layer semiconductor layer.

[0097] Figure 3 A comparison diagram of the fitted thickness and the reference thickness value of a three-layer structure sampled at a single point according to an embodiment of the present invention is shown.

[0098] For a buffer layer + double epitaxial layer structure, 10 single-point repeated samplings were performed to obtain the reflection spectrum, and then the calculated thickness value was fitted. Figure 3 The thickness of the buffer layer, the thickness of the epitaxial layer 1, the thickness of the epitaxial layer 2 and the total thickness of the three-layer structure are shown in the figure.

[0099] The single-point sampling was repeated 10 times, and the thickness of each layer and the total thickness of the buffer layer + double-layer epitaxial layer structure were fitted and calculated using the above method. The 10 results had little difference, indicating that the method of the present invention for calculating the thickness of the doped semiconductor layer using the reflection spectrum fitting has good stability.

[0100] Figure 4 A comparison diagram of the fitted thickness and reference thickness values ​​of a three-layer structure sampled at multiple points according to an embodiment of the present invention is shown.

[0101] For a wafer with substrate + buffer layer, 25 coordinate points are selected on the wafer, and then samples are taken at each coordinate point, the reflection spectrum of each coordinate point is measured, and the thickness of the buffer layer at the 25 coordinate points is calculated by fitting. The results are as follows: Figure 4The thickness of the buffer layer can be measured to 0.05um, and the repeatability is less than 0.02um, indicating that the method of calculating the thickness of the doped semiconductor layer by using the reflection spectrum fitting of the present invention has good stability.

[0102] Although some embodiments of the present invention have been described in this application document, it will be appreciated by those skilled in the art that these embodiments are merely shown as examples. Those skilled in the art may conceive of numerous variations, alternatives, and improvements under the teachings of the present invention without departing from the scope of the present invention. The appended claims are intended to define the scope of the present invention and to cover methods and structures within the scope of these claims themselves and their equivalents.

Claims

1. A method for calculating the thickness of a doped semiconductor layer using reflection spectrum fitting, characterized in that: include: Inputting the reflection spectrum of one or more doped semiconductor layers on the wafer into a mathematical relationship model between reflectivity and thickness, and setting the number of doped semiconductor layers, wherein: in the mathematical relationship model between reflectivity and thickness, the parameters include the number of doped semiconductor layers, the carrier concentration, the carrier mobility and the thickness of each doped semiconductor layer, and the target value is the reflectivity; as well as By adjusting the carrier concentration, carrier mobility and thickness of each doped semiconductor layer, the theoretical spectrum calculated by the mathematical relationship model of reflectivity and thickness is fitted with the reflectance spectrum, and the carrier concentration, carrier mobility and thickness are output.

2. The method according to claim 1, characterized in that In the mathematical relationship model between reflectivity and thickness, the complex dielectric function is calculated from the carrier concentration and the carrier mobility, the complex refractive index is calculated from the complex dielectric function, and the reflectivity is calculated from the complex refractive index and the thickness of the doped semiconductor layer.

3. The method according to claim 2, characterized in that The complex refractive index of each doped semiconductor layer is calculated by using the complex dielectric function of each doped semiconductor layer, and the characteristic matrix of each doped semiconductor layer is calculated by using the complex refractive index and thickness of each doped semiconductor layer; The overall characteristic matrix is ​​obtained by multiplying the characteristic matrices of each doped semiconductor layer; The overall characteristic matrix is ​​multiplied by the incident light to obtain the outgoing light, and the outgoing light is used to calculate the total reflection coefficient, and then the total reflectivity is calculated from the reflection coefficient.

4. The method according to claim 3, characterized in that: The calculation of the complex refractive index of each doped semiconductor layer using the complex dielectric function of each doped semiconductor layer includes: where ∈(ω) is the complex dielectric function, ∈ ∞ is the high frequency dielectric constant, ω p is the plasma frequency, γ is the plasma damping coefficient, ω is the angular frequency of the light wave (ω=2πf), ω is known; Where N is the carrier concentration, e is the electron charge, m* is the effective mass, ε ∞ is the high frequency dielectric constant, ε0 is the vacuum dielectric constant; and where μ is the carrier mobility.

5. The method according to claim 4, characterized in that For a single doped semiconductor layer, the optical path length δ j With wavelength λ, material thickness d j , angle of incidence α j The relationship is When the light wave passes through a single-layer doped semiconductor layer, the light wave With the emitted light wave The relationship is is defined as the characteristic matrix of a doped semiconductor, where: For TE mode, γ j =n j cosα j , δ j =ωn j d j cosα j / c For TM modules: γ j =n j cosα j , δ j =ωn j d j cosα j / c in, α0 is the incident angle, ω is the angular frequency of light, c is the speed of light, d j is the thickness of the corresponding doped semiconductor layer, n j is the refractive index of the corresponding doped semiconductor layer, n0 is the refractive index of air, j is the number of layers corresponding to the multilayer doped semiconductor layer, δ j It is the optical path length of each layer corresponding to the multilayer film.

6. The method according to claim 5, characterized in that For multiple doped semiconductor layers, first calculate the characteristic matrix of each layer, and then multiply them to obtain the overall characteristic matrix M tot , the feature matrix M tot Multiplying the incident light by the outgoing light Where N is a positive integer; The total reflection coefficient is given by the following relationship: Reflection coefficient The total reflectivity is calculated from the total reflection coefficient: R = |r| 2 .

7. The method according to claim 1, characterized in that The carrier concentration, carrier mobility and thickness of each doped semiconductor layer are automatically adjusted using the least squares method or genetic algorithm.

8. The method according to claim 1, characterized in that Before inputting the reflection spectrum into the mathematical relationship model of reflectivity and thickness, the method also includes: obtaining the reflection spectrum of one or more doped semiconductor layers on the wafer.

9. The method according to claim 8, characterized in that Obtaining the reflectance spectrum of one or more doped semiconductor layers on a wafer involves: Using a Fourier transform infrared spectrometer to measure the interference spectrum of the wafer and the interference spectrum of the reference piece; Converting the interference spectrum of the wafer and the interference spectrum of the reference piece into corresponding single-beam spectrum of the wafer and single-beam spectrum of the reference piece by Fourier transform; and The reflection spectrum of one or more doped semiconductor layers is obtained by subtracting the ordinate of the single beam spectrum of the reference wafer from the ordinate of the single beam spectrum of the wafer.

10. The method according to any one of claims 1 to 9, characterized in that: The single-layer doped semiconductor layer is a buffer layer, and the multiple-layer doped semiconductor layers are a buffer layer and a single-layer epitaxial layer or a buffer layer and a double-layer epitaxial layer.

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